Antiviral agent comprising recombinant mistletoe lectins

ABSTRACT

The invention relates to an antiviral agent containing recombinant mistletoe lectins for treating virus infections and to a medicament and/or pharmaceutical composition for treating virus infections.

The invention relates to an antiviral agent comprising recombinant mistletoe lectins for treating virus infections, and to a medicinal drug and/or a pharmaceutical composition for treating virus infections.

When virus infections occur, viruses penetrate the organism, where they replicate. The reaction of the organism that generally ensues can manifest itself in an infectious disease. A large number of diseases can be caused by viruses in humans. At present, preventive immunizations are only possible against a limited number of virus infections. Because viruses, contrary to bacteria, are not cells, they cannot be destroyed as bacteria can be. It is only possible to inhibit or prevent a viral infection and virus replication.

An infection with Herpes simplex viruses will be described hereafter by way of example for the large number of possible virus diseases.

Herpes simplex viruses are common worldwide and humans are the only natural host to them, serving as a reservoir. In Germany, antibodies against Herpes simplex viruses were detected in 84 to 92% of persons of an age-normalized random sample analysis. Diseases caused by the Herpes simplex virus are among the most frequent infectious diseases of the skin. The majority of infections occur on the face and in the genital region. It is commonly known that the Herpes simplex virus is a recurring virus infection, which is characterized by the appearance of individual or multiple accumulations of small vesicles on the skin or mucous membranes.

There are two primary types of the Herpes simplex virus (HSV)—HSV 1 and HSV 2. They differ slightly from each other in terms of their disease patterns and disease localizations. Clinically different HSV infections are distinguished according to the occurrence and localization of the disease symptoms, with the most important ones being Herpes simplex labialis (oral herpes) and Herpes simplex genitalis. After an initial infection, the virus will always remain in the organism in a dormant state (latency), which is referred to as a persistent infection. The treatment of HSV infections cannot end this persistence, but attempts to prevent the replication of the virus after reactivation from latency has occurred.

The treatment of virus infections includes the use of active ingredients, which are subsumed under the term ‘virostatic agents’. These medicinal drugs intervene in the replication of viruses in various respects and thus prevent further spreading of the pathogen. The virostatic agents frequently employed for fighting Herpes simplex viruses in the case of oral herpes belong to the group known as nucleoside analogs. These inhibit DNA synthesis and consequently replication of the viruses. Because nucleoside analogs always intervene in virus replication, they work only with actively reproducing viruses. Among these nucleoside analogs, the compound known as Aciclovir has proven to be effective, however it also has some side effects. Aciclovir is eliminated via the kidneys. Renal problems were found with high dosages that were administered quickly and intravenously, because Aciclovir can then crystallize out in the kidneys. Aciclovir can also be incorporated into cellular DNA and thus constitutes a chromosome mutagen. Additionally, resistances may develop.

While nucleoside analogs are highly valuable, a need remains for improved medicinal drugs so as to be able to better treat the symptoms that occur by the outbreaks of virus infections.

Additionally, some viruses exist, which favor the development of cancer because they cause a latent infection over an extended period. For example, papilloma viruses have been linked to cervical cancer, and the Epstein-Barr virus to nasopharyngeal cancer.

Mistletoe extracts have been used therapeutically for centuries. Mistletoe preparations have been employed notably in cancer therapy with varying success (Bocci V 1993 J Biol Regulators and Homeostatic Agents 7(1): 1-6; Gabius H-J, Gabius S, Joshi S S et al. 1993 Planta Med 60: 2-7; Gabius H-J & Gabius S 1994 PZ 139: 9-16; Ganguly C & Das S 1994 Chemotherapy 40: 272-278, Hajto T, Hostanska K, Gabius_J 1989 Cancer Res 49: 4803-4808, Hajto T, Hostanska K, Frei K et al. 1990 Cancer Res. 50: 3322-3326). It was found that the therapeutic effects are induced in particular by so-called mistletoe lectins (viscumin, Viscum album agglutinin, VAA). In addition to a cytotoxic effect, the mistletoe lectins reportedly also cause nonspecific immune stimulation, the positive effects of which are used for the treatment of tumor patients. Various analyses conducted with mistletoe lectins in vitro (Hajto et al., 1990 (supra); Mannel D N, Becker H, Gundt A et al. 1991 Cancer Immunol Immunother 33: 177-182; Beuth J, Ko K L, Tunggal L et al. 1993 Drug Res 43: 166-169) and in vivo (Hajto T 1986 Oncology 43 suppl 1: 51-65; Hajto et al., 1989 (supra), Beuth J, Ko H L, Gabius H-J et al. 1991 In Vivo 5: 29-32; Beuth J, Ko H L, Gabius H-J et al. 1992 J Clin Invest 70: 658-661) as well as clinical studies (Beuth et al., 1992 (supra)) showed an increased release of inflammatory cytokines (TNF-alpha, IL-1, IL-6) and an activation of cellular components of the immune system (Th cells, NK cells).

Only few studies have previously analyzed the antiviral effectiveness of native mistletoe lectins, which represent extracts from mistletoe lectins. Karagöz et al. (Phytother. Res. 17, 560-562, 2003) previously analyzed the antiviral effectiveness of extracts of European mistletoe (Viscum album L.). Karagöz et al explored whether different mistletoe extracts have an antiviral effectiveness for the human parainfluenza virus type 2 (HPIV-2). To this end, the following mistletoe extracts were analyzed: an aqueous extract, an ethanol extract, a petroleum ether extract, a chloroform extract and an acetone extract. The test system consisted of Vero cells, the human HPIV-2 and the different mistletoe extracts. Cytotoxicity tests and plaque assays were carried out. It was shown that the aqueous extract had a significant effect against the replication of HPIV-2, while the chloroform extract had moderate activity. The remaining extracts showed no significant effect on the replication of HPIV-2.

The mistletoe extracts described in the related art are multi-substance mixtures of plant origin, the ingredients of which are not described nor characterized. The analyses conducted by Karagöz et al. therefore do not clarify which substances in the aqueous extract exhibited the activity against HPIV-2 replication. The composition of the ingredients of plant extracts is heterogeneous. As a result, difficulties exist with adjusting extracts to particular concentrations of one or more ingredients in terms of a pharmacological effect.

Previously, three mistletoe lectins (ML-I, ML-II, ML-III) having different molecular weights and sugar-binding specificities were identified by way of analyses of the mistletoe extract. It was shown that the immune-stimulating effect of the mistletoe extract can be attributed to ML-I. The ML-I lectin has two glycosylated A- and B-chains (MLA and MLB). The A-chain is responsible for an enzymatic inactivation of ribosomes (Endo et al., 1988), while the B-chain is involved in carbohydrate binding. The two chains are linked to each other by disulfide bridges. The resulting mistletoe lectin monomers can join together to form dimers, forming non-covalent bonds.

It is now also possible to produce recombinant biologically active mistletoe lectin. EP 0 751 221 describes the preparation of mistletoe lectin polypeptides as a structurally homogeneous substance in pure form, wherein, starting from the gene sequences of the mistletoe lectin, recombinant, highly pure individual chains (A-chain, B-chain) are produced, which can be reassociated in vitro and thus result in a recombinant mistletoe lectin holoprotein, which is homogeneous in terms of its protein chemistry, enzymatic activity and structure, this being so-called Aviscumin. According to EP 0 751 221, the recombinant mistletoe lectin polypeptide is useful for therapeutic purposes both as a holoprotein, as a partial chain and in the form of subfragments and is covered by the invention.

Previously, recombinant mistletoe lectins were used in particular for the treatment of tumor diseases. While EP 0 751 221 mentions that recombinant mistletoe lectins can also conceivably be used for treating infectious diseases, no suggestions are disclosed that a treatment of virus infections with recombinant mistletoe lectins is effective.

It is the object of the present invention to provide antiviral agents, which can be used to effectively treat virus infections. Another object of the present invention is to provide a medicinal drug and pharmaceutical compositions for treating virus infections.

The object is achieved by the provision of an antiviral agent, as well as by the provision of a medicinal drug and a pharmaceutical composition, wherein these comprise recombinant mistletoe lectins for the treatment and prophylaxis of virus infections, wherein the recombinant mistletoe lectins comprise the amino acid sequences below.

The antiviral agent according to the invention preferably comprises the mistletoe lectin A-chain (MLA) and the mistletoe lectin B-chain (MLB), either individually or together, including in the form of dimers (see, for example, EP 0 751 221 or EP 1 051 495).

The recombinant mistletoe lectin polypeptide of the mistletoe lectin A-chain comprises the following sequences: SEQ ID Nos. 1-3, including the isoforms thereof or a functional fragment thereof.

The recombinant mistletoe lectin polypeptide of the mistletoe lectin B-chain comprises the following sequences: SEQ ID Nos. 4-12, including the isoforms thereof or a functional fragment thereof.

(hereafter collectively referred to as “recombinant mistletoe lectins”).

Additionally, Aviscumin is preferred, a heterodimer composed of the sequences SEQ ID No. 1 and SEQ ID No. 4.

The invention relates to an antiviral agent comprising recombinant mistletoe lectin for use with virus infections or so as to prevent virus infections, wherein the recombinant mistletoe lectin is selected from the group of the amino acid sequences SEQ ID Nos. 1-12, or comprises parts and fragments thereof, or a combination thereof.

In the context of the present invention, the term “functional fragment” defines fragments of said polypeptides, which have the same biological function as the polypeptide implemented above with the respective amino acid sequence.

The term “same biological function” in this context describes, for example, that fragments or derivatives of the polypeptides induce the same signals in a cell as said peptides. Examples of fragments include peptide domains having defined functions. The “same biological function” also encompasses cytotoxicity, immune stimulation (both of the native and of the adaptive immune system), stimulation of the release of cytokines, antigenicity, induction of the expression or activation of surface markers, induction of apoptosis, or endorphin stimulation.

The expression “biological activity of the recombinant mistletoe lectin” shall be understood here to mean any biological activity from the spectrum of all the biological activities of the recombinant mistletoe lectin. For example, such a function is the pharmacological effect of the recombinant mistletoe lectin.

Analyses of ML-I monomers showed 25 different isoforms, which can be attributed to different combinations of various A- and B-chains as well as different glycosylation states of the chains.

The present invention therefore also relates to a mistletoe lectin polypeptide or a fragment thereof, which according to the invention comprises the sequence variability of the different MLA and MLB chains for the sequences SEQ ID Nos. 1-12.

The antiviral agent according to the invention preferably includes a recombinant mistletoe lectin polypeptide having the sequences SEQ ID Nos. 1-12, or a functional fragment thereof, or any arbitrary combination thereof.

As was already mentioned above, recombinant mistletoe lectins previously were used primarily for the treatment of tumor diseases. However, to this day, it has not been shown that recombinant mistletoe lectins have an effect on virus infections. The invention surprisingly showed that recombinant mistletoe lectins can be effectively used against virus infections, as the examples impressively show. The cytotoxicity of the sequences according to the invention, in particular Aviscumin, is already 0.5 ng/plaque.

Compared to the mistletoe lectins in the related art, the recombinant mistletoe lectins particularly advantageously include no impurities, so that even a lower dosage has increased effectiveness. Moreover, recombinant mistletoe lectins allow high dosage precision to be achieved, whereby successful (locally) specific antiviral treatment is possible.

The antiviral agent according to the invention is therefore used for treating one of the following virus infections: Herpes simplex virus infection, adenovirus infection, poliovirus infection, poxvirus infection, parvovirus infection, papovavirus infection, hepadnavirus infection, orthomyxovirus infection, papilloma virus infection, paramyxovirus infection, coronavirus infection, picornavirus infection, reovirus infection, togavirus infection, flavivirus infection, arenavirus infection, rhabdovirus infection, and retrovirus infection.

The invention further relates to the treatment of skin virus warts, anogential warts, mucous membrane warts and malignant tumors such as cervical cancer, penis and vulvar cancer, in particular as part of a papilloma virus infection (HPV).

The invention also relates to a medicinal drug for treating virus infections, comprising the recombinant mistletoe lectin polypeptide, optionally together with a pharmaceutically compatible carrier. Examples of particularly suitable pharmacologically compatible carriers are known to a person skilled in the art and include buffered salt solutions, water, emulsions such as oil/water emulsions, different types of detergents, sterile solutions, and the like. Medicinal drugs that include such carriers can be formulated by way of known conventional methods. These medicinal drugs can be administered to an individual in a suitable dosage. The administration can take place locally, orally or parenterally, for example, intravenously, intraperitoneally, subcutaneously, intramuscularly, locally, intranasally, intrabronchially or intradermally, or via a catheter in a location of an artery. The type of dosage is determined by the treating physician based on the clinical factors. It is known to a person skilled in the art that the type of dosage is dependent on various factors, for example the body size or the weight, the body surface, the age, the gender or the general state of health of the patient, but also the agent to be specifically administered, the duration and type of administration, and other medicinal drugs that may be administered at the same time.

The invention further relates to a pharmaceutical composition, comprising the recombinant mistletoe lectin polypeptides according to the invention. The composition can be administered locally or systemically. Preparations for a parenteral administration include sterile aqueous or non-aqueous solutions, suspensions and emulsions. Examples of non-aqueous solutions include propylene glycol, polyethylene glycol, vegetable oils such as olive oil, and organic ester compounds such as ethyl oleate, which are suitable for injections. Aqueous carriers include water, alcoholic aqueous solutions, emulsions, suspensions, salt solutions and buffered media. Parenteral carriers include sodium chloride solutions, Ringer's dextrose, dextrose, and sodium chloride, Ringer's lactate and bound oils. Intravenous carriers include, for example, liquid, nutrient and electrolyte supplements (such as those based on Ringer's dextrose).

The composition according to the invention can also include preservatives and other additives, such as antimicrobial compounds, antioxidants and complexing agents. Moreover, compounds such as interleukins, interferons or a non-specific immune modulatory agent may be present. Cytostatic agents, antibiotics and combinations thereof may likewise be present.

According to the invention, the pharmaceutical composition is used for treating the virus infections described above.

The composition according to the invention is preferably present as a solution, gel or cream.

The invention further relates to the use of a recombinant mistletoe lectin for producing an antiviral agent for treating said virus infections. The treatment preferably comprises the administration of a therapeutically effective quantity of the recombinant mistletoe lectin to a person who has contracted, or is expected to contract, an infection.

The effectiveness of the invention for treating virus infections will be described based on the following analysis by way of example.

The following examples are provided to describe the invention, without limiting the invention to these examples.

EXAMPLES

Vero cells (renal cells from African green monkeys) and BGM cells (renal cells from Borgio green monkeys) were incubated for 2 hours with Herpes simples viruses type 1 (HSV-1) as part of a log₁₀ dilution series. The virus was removed after the cells were infected. The recombinant mistletoe lectin was diluted with cell culture medium, which was used both with and without interfering substances. The interfering substances used were 10% fetal calf serum (FCS) and 3% bovine serum albumin with sheep erythrocytes. 200 μl of the solution with recombinant mistletoe lectin was applied per well to the infected cells. Cell culture medium was applied to the infected cells for virus control purposes. Aciclovir (1.5 mmol) was used in place of the recombinant mistletoe lectin as a negative control substance against HSV-1. The cells were incubated at 37° C.+/−1° C. for 2 to 7 days.

After incubation, the cells were analyzed for cytopathic effects (CPE) using an inverted microscope, and the 50% infectious dose, based on a cell culture, TCID₅₀/ml (tissue culture infectious dose) was determined. If no cytopathic effects were visible, this meant that the viruses had been successfully inactivated by the recombinant mistletoe lectin.

So as to gain a more detailed impression of the virus reduction, a plaque reduction assay was conducted, so as to determine the antiviral effectiveness of the recombinant mistletoe lectin. For this purpose, the Vero cells/BGM cells were placed in 12-well plates.

The semi-adherent cells were incubated for 2 hours with a log₁₀ dilution series of the HSV-1 (100 μl per well). The virus was removed after the cells were infected. The recombinant mistletoe lectin was diluted with cell culture medium (with and without interfering substances) and mixed 1:1 with warm agarose. The interfering substances used were fetal calf serum and sheep erythrocytes.

2 ml of the solution comprising the recombinant mistletoe lectin was applied to the infected cells. Cell culture medium was applied to the infected cells for virus control purposes. Aciclovir (1.5 mmol) was used in place of the recombinant mistletoe lectin as a negative control substance against HSV-1. After gelling of the agarose, the cells were incubated at 37° C.+/−1° C. for 7 days. After the incubation period, the cells were fixed for 4 hours with methanol comprising 4% sodium chloride. The cells were then dyed with crystal violet. The virus-induced plaque was counted under the microscope and the TCID₅₀/ml was determined.

The following validation steps were conducted as part of this analysis:

-   -   identification of the suitable virus titer with the         corresponding cell line;     -   identification of the concentration of recombinant mistletoe         lectin that is tolerated by the corresponding cell line by         measurement of the cytotoxicity and vitality;     -   identification of the concentration of recombinant mistletoe         lectin that leaves the cell line vulnerable to a virus         infection.

Results:

The analysis surprisingly showed an antiviral effectiveness of recombinant mistletoe lectin against HSV-1 and against adenovirus type 5. In the suspension assay with HSV-1/BGM cells, a concentration of 50 ng/ml of recombinant mistletoe lectin caused a virus titer reduction of 2.43 log₁₀ without interfering substances and without the use of MicroSpin columns (see Table 2). A concentration of 500 ng/ml of recombinant mistletoe lectin produced a virus titer reduction of 2.57 log₁₀ and 3.29 log₁₀ when using MicroSpin columns and FCS as the interfering substance (see Table 2).

In the plaque reduction assay, an average relative inhibition of the HSV-1 infection of 17.04% was shown at a concentration of 0.5 ng/ml of recombinant mistletoe lectin (without MicroSpin filtration), and an average relative inhibition of the HSV-1 infection of 7.41% was shown with MicroSpin filtration (see Table 3).

The average relative inhibition of the adenovirus type 5 infection in the plaque reduction assay was 79.7% at a concentration of 0.5 ng/ml recombinant mistletoe lectin (without MicroSpin filtration), and 22.2% with MicroSpin filtration (see Table 4).

TABLE 1 Results of the cytotoxicity tests of the test cells BGM BGM with without Vero MicroSpin MicroSpin Vero with without 7 days 7 days Cell Line MicroSpin MicroSpin incubation incubation Recombinant mistletoe cytotoxic cytotoxic n.t. n.t. lectin 5000 ng/ml Recombinant mistletoe cytotoxic cytotoxic cytotoxic cytotoxic lectin 500 ng/ml Recombinant mistletoe cytotoxic cytotoxic negative negative lectin 50 ng/ml Recombinant mistletoe negative cytotoxic negative negative lectin 5 ng/ml Recombinant mistletoe negative negative negative negative lectin 0.5 ng/ml Recombinant mistletoe negative negative negative negative lectin 0.05 ng/ml Recombinant mistletoe n.t. n.t. negative negative lectin 0.005 ng/ml Negative control n.t. negative n.t. negative substance n.t. = not tested

TABLE 2 Test for antiviral effectiveness of recombinant mistletoe lectin with HSV-1, host BGM cells (cell suspension) Virus titer HSV-1 Virus reduction (log₁₀) + (TCID₅₀/ml) 95% conf. limits Virus control 10^(−6.64+/−0.46) — 10^(−6.93+/−0.36) Recombinant oSS, without 10^(−6.79+/−0.36) no virus titer reduction mistletoe lectin MicroSpin  5 ng/ml oSS, with 10^(−6.79+/−0.36) no virus titer reduction MicroSpin FCS, without 10^(−6.79+/−0.54) no virus titer reduction MicroSpin FCS, with 10^(−6.64+/−0.46) no virus titer reduction MicroSpin Recombinant oSS, without 10^(−4.21+/−0.54) 2.43 +/− 0.71 mistletoe lectin MicroSpin  50 ng/ml oSS, with 10^(−6.36+/−0.56) 0.28 +/− 0.72 MicroSpin FCS, without 10^(−6.36+/−0.54) 0.28 +/− 0.65 MicroSpin FCS, with 10^(−6.36+/−0.46) 0.28 +/− 0.65 MicroSpin Recombinant FCS, with 10^(−4.07+/−0.49) 2.57 +/− 0.67 mistletoe lectin MicroSpin    500 ng/ml ≦10^(−3.64+/−0.28)   ≧3.29 +/− 0.54   oSS = without interfering substances

TABLE 3 Test for antiviral effectiveness of recombinant mistletoe lectin, plaque assay with HSV- 1 on Vero cells Recombinant mistletoe lectin Aciclovir 0.5 ng/ml 0.5 ng/ml 0.5 ng/ml Virus dilution Virus control (1.5 mmol) without Spin with Spin with Spin 10^(−5.0) Number of >50, >50, 6 0, 0, 0 >50, >50, 10, >50, cytotoxic plaque >50 >50 Mean value >35 0 >50 >36 StabW n.d. 0 n.d. n.d. n.d. Relative 100 0 100 100 n.d. infectiosity Relative 0 100 0 0 n.d. inhibition 10^(−5.48) Number of 5, 5, 4, 4 0, 0, 0, 0 6, 5, 3, 2 3, 4, 4, 3 cytotoxic plaque Mean value 4.5 0 4.0 3.5 StabW 0.57 0 1.82 0.57 n.d. Relative 100 0 88.88 77.77 n.d. infectiosity Relative 0 100 11.12 22.23 n.d. inhibition Number of 2, 3, 3, 2 0, 0, 0, 0 1, 2, 1, 2 2, 3, 1, 4 cytotoxic plaque Mean value 2.5 0 1.5 2.5 10^(−5.95) StabW 0.57 0 0.57 1.29 n.d. Relative 100 0 60.0 100 n.d. infectiosity Relative 0 100 40.0 0 n.d. inhibition Average relative n.a. 100 17.04 7.41 n.d. inhibition n.d. = not detectable n.a. = not to be evaluated

TABLE 4 Test for antiviral effectiveness of recombinant mistletoe lectin, plaque assay with adenovirus type 5 on BGM cells Recombinant mistletoe lectin 0.5 ng/ml Virus without 0.5 ng/ml 0.5 ng/ml Virus dilution control Spin with Spin with Spin 10^(−4.0 ) Number of 5, 5, 8 2, 3, 0 11, 8, 8 cytotoxic plaque Mean value 6 1.66 9 StabW 1.7 1.52 1.73 n.d. Relative 100 27.7 100 n.d. infectiosity Relative 0 72.3 0 n.d. inhibition Number of 3, 4, 2, 3 0, 0, 0, 0 4, 2, 2, 4 cytotoxic plaque 10^(−4.46) Mean value 3 0 3 StabW 0.81 0 1.15 n.d. Relative 100 0 100 n.d. infectiosity Relative 0 100 0 n.d. inhibition Number of 1, 1, 2, 2 0, 0, 2, 0 0, 0, 0, 2 cytotoxic plaque Mean value 1.5 0.5 0.5 10^(−4.95) StabW 0.57 1.0 1.0 n.d. Relative 100 33.3 33.3 n.d. infectiosity Relative 0 66.7 66.7 n.d. inhibition Average relative n.a. 79.7 22.2 n.d. inhibition n.d. = not detectable n.a. = not to be evaluated 

1-10. (canceled)
 11. A method of treating a viral infection comprising administering to a patient with a viral infection a drug containing a recombinant mistletoe lectin, wherein the recombinant mistletoe lectin is a mistletoe lectin A-chain selected from the group consisting of the amino acid sequences of SEQ ID NO: 1-3, or comprises parts and fragments thereof, or is a combination thereof.
 12. The method of claim 11, wherein a cytotoxicity of recombinant mistletoe lectin is less than 0.5 ng/plaque.
 13. The method of claim 11, wherein the viral infection is selected from the group consisting of: Herpes simplex virus infection, adenovirus infection, poliovirus infection, poxvirus infection, parvovirus infection, papovavarius infection, hepadnavirus infection, orthomyxovirus infection, papilloma virus infection, paramyxovirus infection, coronavirus infection, picornavirus infection, reovirus infection, togavirus infection, flavivurs infection, arenavirus infection, rhabdovirus infection, and retrovirus infection.
 14. The method of claim 11, wherein the drug further comprises a pharmaceutically acceptable carrier.
 15. The method of claim 11, wherein the drug further comprises interleukins, interferons, a cytostatic agent.
 16. The method according to claim 11, wherein the recombinant mistletoe lectin further comprises a mistletoe lectin B-chain selected from the group consisting of amino acid sequences of SEQ ID NOs: 4-12, or comprises parts and fragments thereof, or is a combination thereof.
 17. The method according to claim 1, wherein the recombinant mistletoe lectin further comprises a mistletoe lectin A-chain of amino acid sequence of SEQ ID NO: 1 and further comprises the mistletoe lectin B-chain of amino acid sequence SEQ ID NO:
 4. 18. A method of contacting a cell infected with Herpes simplex virus with a drug containing a recombinant mistletoe lectin, wherein the recombinant mistletoe lectin is a mistletoe lectin A-chain selected from the group consisting of the amino acid sequences of SEQ ID NO: 1-3, or comprises parts and fragments thereof, or is a combination thereof.
 19. The method of claim 18, wherein the drug is administered at a concentration of 50 ng/ml.
 20. The method of claim 18, wherein the drug is administered at a concentration of 0.5 ng/ml.
 21. The method according to claim 18, wherein the recombinant mistletoe lectin further comprises a mistletoe lectin B-chain selected from the group consisting of amino acid sequences of SEQ ID NOs: 4-12, or comprises parts and fragments thereof, or is a combination thereof.
 22. A method of preventing a viral infection comprising administering to a patient with a viral infection a drug containing a recombinant mistletoe lectin, wherein the recombinant mistletoe lectin is a mistletoe lectin A-chain selected from the group consisting of the amino acid sequences of SEQ ID NO: 1-3, or comprises parts and fragments thereof, or is a combination thereof.
 23. The method according to claim 22, wherein the recombinant mistletoe lectin further comprises a mistletoe lectin B-chain selected from the group consisting of amino acid sequences of SEQ ID NOs: 4-12, or comprises parts and fragments thereof, or is a combination thereof. 